3D printers were born in the mid 1980s, and were first invented by American scientists. A 3D printer is an apparatus that uses 3D printing technology to produce a device of the real object. The basic principle for 3D printing is using special materials (resin or powder, etc.) to manufacture real 3D models that are designed in computer, and by aggradation of the binder, each layer of printing material are bobbed to form the designed shape, and the 3D objects are finally printed out. The rapid prototype manufacturing technology is widely applied in the model manufacture in the stage of product development because of the fast manufacturing and low cost. 3D printing is a kind of rapid prototyping technology. It first transfers the objects into 3D data, and then uses the adhesive materials such as powdered metal, plastic and so on to print them layer by layer. The model manufacturing and industrial design are used to build models. They are now becoming product manufacturing and forming “Direct Digital Manufacturing.” A variety of the rapid manufacturing technologies have been developed such as the Stereo Lithography Appearance (SLA), the Laminated Object Manufacturing (LOM), the Fused Deposition Modeling (FDM), the Selective Laser Sintering (SLS), the Three-Dimensional Printing (3DP), and the Digital Light Procession (DLP) etc. However, in the current situation, the accuracy of FDM is poor, and it is necessary to continuously melt the material wire and wait for the material to cure, and the overall molding speed is slow. The SLA technology is limited by the optical characteristics of galvanometers. Generally, the galvanometer-type printing surface is less than 300 mm*300 mm. Area dynamic focusing system is required if the size of the printing area is more than 300 mm*300 mm. and it will greatly raise the cost. The principle of the galvanometer system determines that the larger the printing area, the longer the focal length, and the larger the spot, the more laser energy is wasted. The DLP technology is similar to a projector's principle, in which the most important component is the DMD chip. The biggest advantage of DLP is that it can be exposed layer by layer. Theoretically, it is very fast. However, if a larger printing area is required and the high power density of the curing light is required simultaneously, the light intensity must be greatly increased, but the DMD cannot withstand the high light intensity, and the heat dissipation of the system becomes a serious problem if the light intensity increases. Therefore, 3D printing based on DLP technology developed slowly in the direction of large printing area.
Because the energy radiated from each DLP projector is non-uniform light energy, using multiple projectors will inevitably cause uneven distribution of the illumination intensity on each projectors, and it will also affect the overlapped area on the printing area, and aggravate the non-uniformity of the energy.